1. Field of the Invention
This invention relates to a vehicle seat having a head restraint apparatus.
2. Description of the Related Art
Proposed is a movable head restraint apparatus in which a head rest can be moved forward to restrain the head of an occupant in case of a rear-end collision of a vehicle or the like. A vehicle seat structure described in Jpn. Pat. Appln. KOKAI Publication No. 2001-163099 (patent document 1), for example, comprises guide pins that are arranged under stays of a head rest and slots in which the guide pins are fitted individually. The slots extend in the vertical direction. This prior art example is provided with passive means that is actuated by an inertial load of the occupant's body at the time of collision. The passive means causes guide pins to move upward along the slots. In this arrangement, the head rest tilts forward as it moves upward.
In a seat back described in Jpn. Pat. Appln. KOKAI Publication No. 2000-210155 (patent document 2), moreover, a pressure receiving member is provided at the back of a pad. In case of collision, an armature pipe is pushed up by the pressure receiving member. In this prior art example, a vertically intermediate portion of the armature pipe moves forward and upward at the time of collision. Thus, the head rest tilts forward as it moves upward.
In the structures described in the patent documents 1 and 2, that part of the head rest which corresponds to the under-neck region of the occupant's body moves forward the moment the occupant's body is pressed against the seat back at the time of collision. Accordingly, the under-neck region tends to be restrained before the occupant's head is restrained by the head rest. Thus, the head rest is hindered from moving in a desired direction (or forward and upward). Besides, the under-neck region is inevitably restrained earlier than the head, so that the effect of the head restraint cannot be fully enjoyed.
In the conventional movable head restraint apparatus described above, moreover, the stays of the head rest are easily returned back by a load (horizontal rearward load) from the occupant's head that acts on the head rest after the head rest abuts against the head. Thus, the head restraint is inadequate.